Wafer dicing using femtosecond-based laser and plasma etch

ABSTRACT

Methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits, are described. A method includes forming a mask above the semiconductor wafer. The mask is composed of a layer covering and protecting the integrated circuits. The mask is patterned with a femtosecond-based laser scribing process to provide a patterned mask with gaps. The patterning exposes regions of the semiconductor wafer between the integrated circuits. The semiconductor wafer is then etched through the gaps in the patterned mask to singulate the integrated circuits.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/357,468, filed Jun. 22, 2010, the entire contents of which are herebyincorporated by reference herein.

BACKGROUND

1) Field

Embodiments of the present invention pertain to the field ofsemiconductor processing and, in particular, to methods of dicingsemiconductor wafers, each wafer having a plurality of integratedcircuits thereon.

2) Description of Related Art

In semiconductor wafer processing, integrated circuits are formed on awafer (also referred to as a substrate) composed of silicon or othersemiconductor material. In general, layers of various materials whichare either semiconducting, conducting or insulating are utilized to formthe integrated circuits. These materials are doped, deposited and etchedusing various well-known processes to form integrated circuits. Eachwafer is processed to form a large number of individual regionscontaining integrated circuits known as dice.

Following the integrated circuit formation process, the wafer is “diced”to separate the individual die from one another for packaging or for usein an unpackaged form within larger circuits. The two main techniquesthat are used for wafer dicing are scribing and sawing. With scribing, adiamond tipped scribe is moved across the wafer surface along pre-formedscribe lines. These scribe lines extend along the spaces between thedice. These spaces are commonly referred to as “streets.” The diamondscribe forms shallow scratches in the wafer surface along the streets.Upon the application of pressure, such as with a roller, the waferseparates along the scribe lines. The breaks in the wafer follow thecrystal lattice structure of the wafer substrate. Scribing can be usedfor wafers that are about 10 mils (thousandths of an inch) or less inthickness. For thicker wafers, sawing is presently the preferred methodfor dicing.

With sawing, a diamond tipped saw rotating at high revolutions perminute contacts the wafer surface and saws the wafer along the streets.The wafer is mounted on a supporting member such as an adhesive filmstretched across a film frame and the saw is repeatedly applied to boththe vertical and horizontal streets. One problem with either scribing orsawing is that chips and gouges can form along the severed edges of thedice. In addition, cracks can form and propagate from the edges of thedice into the substrate and render the integrated circuit inoperative.Chipping and cracking are particularly a problem with scribing becauseonly one side of a square or rectangular die can be scribed in the <110>direction of the crystalline structure. Consequently, cleaving of theother side of the die results in a jagged separation line. Because ofchipping and cracking, additional spacing is required between the diceon the wafer to prevent damage to the integrated circuits, e.g., thechips and cracks are maintained at a distance from the actual integratedcircuits. As a result of the spacing requirements, not as many dice canbe formed on a standard sized wafer and wafer real estate that couldotherwise be used for circuitry is wasted. The use of a saw exacerbatesthe waste of real estate on a semiconductor wafer. The blade of the sawis approximate 15 microns thick. As such, to insure that cracking andother damage surrounding the cut made by the saw does not harm theintegrated circuits, three to five hundred microns often must separatethe circuitry of each of the dice. Furthermore, after cutting, each dierequires substantial cleaning to remove particles and other contaminantsthat result from the sawing process.

Plasma dicing has also been used, but may have limitations as well. Forexample, one limitation hampering implementation of plasma dicing may becost. A standard lithography operation for patterning resist may renderimplementation cost prohibitive. Another limitation possibly hamperingimplementation of plasma dicing is that plasma processing of commonlyencountered metals (e.g., copper) in dicing along streets can createproduction issues or throughput limits.

SUMMARY

Embodiments of the present invention include methods of dicingsemiconductor wafers, each wafer having a plurality of integratedcircuits thereon.

In an embodiment, a method of dicing a semiconductor wafer having aplurality of integrated circuits includes forming a mask above thesemiconductor wafer, the mask composed of a layer covering andprotecting the integrated circuits. The mask is then patterned with afemtosecond-based laser scribing process to provide a patterned maskwith gaps, exposing regions of the semiconductor wafer between theintegrated circuits. The semiconductor wafer is then etched through thegaps in the patterned mask to singulate the integrated circuits.

In another embodiment, a system for dicing a semiconductor waferincludes a factory interface. A laser scribe apparatus is coupled withthe factory interface and includes a femtosecond-based laser. A plasmaetch chamber is also coupled with the factory interface.

In another embodiment, a method of dicing a semiconductor wafer having aplurality of integrated circuits includes forming a polymer layer abovea silicon substrate. The polymer layer covers and protects integratedcircuits disposed on the silicon substrate. The integrated circuits arecomposed of a layer of silicon dioxide disposed above a layer of low Kmaterial and a layer of copper. The polymer layer, the layer of silicondioxide, the layer of low K material, and the layer of copper arepatterned with a femtosecond-based laser scribing process to exposeregions of the silicon substrate between the integrated circuits. Thesilicon substrate is then etched through the gaps to singulate theintegrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a top plan of a semiconductor wafer to be diced, inaccordance with an embodiment of the present invention.

FIG. 2 illustrates a top plan of a semiconductor wafer to be diced thathas a dicing mask formed thereon, in accordance with an embodiment ofthe present invention.

FIG. 3 is a Flowchart representing operations in a method of dicing asemiconductor wafer including a plurality of integrated circuits, inaccordance with an embodiment of the present invention.

FIG. 4A illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 302of the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention.

FIG. 4B illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 304of the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention.

FIG. 4C illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 306of the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention.

FIG. 5 illustrates the effects of using a laser pulse in the femtosecondrange versus longer pulse times, in accordance with an embodiment of thepresent invention.

FIG. 6 illustrates a cross-sectional view of a stack of materials thatmay be used in a street region of a semiconductor wafer or substrate, inaccordance with an embodiment of the present invention.

FIG. 7 includes a plot of absorption coefficient as a function of photonenergy for crystalline silicon (c-Si), copper (Cu), crystalline silicondioxide (c-SiO2), and amorphous silicon dioxide (a-SiO2), in accordancewith an embodiment of the present invention.

FIG. 8 is an equation showing the relationship of laser intensity for agiven laser as a function of laser pulse energy, laser pulse width, andlaser beam radius.

FIGS. 9A-9D illustrate cross-sectional views of various operations in amethod of dicing a semiconductor wafer, in accordance with an embodimentof the present invention.

FIG. 10 illustrates compaction on a semiconductor wafer achieved byusing narrower streets versus conventional dicing which may be limitedto a minimum width, in accordance with an embodiment of the presentinvention.

FIG. 11 illustrates freeform integrated circuit arrangement allowingdenser packing and, hence, more die per wafer versus grid alignmentapproaches, in accordance with an embodiment of the present invention.

FIG. 12 illustrates a block diagram of a tool layout for laser andplasma dicing of wafers or substrates, in accordance with an embodimentof the present invention.

FIG. 13 illustrates a block diagram of an exemplary computer system, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Methods of dicing semiconductor wafers, each wafer having a plurality ofintegrated circuits thereon, are described. In the followingdescription, numerous specific details are set forth, such asfemtosecond-based laser scribing and plasma etching conditions andmaterial regimes, in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent to one skilledin the art that embodiments of the present invention may be practicedwithout these specific details. In other instances, well-known aspects,such as integrated circuit fabrication, are not described in detail inorder to not unnecessarily obscure embodiments of the present invention.Furthermore, it is to be understood that the various embodiments shownin the Figures are illustrative representations and are not necessarilydrawn to scale.

A hybrid wafer or substrate dicing process involving an initial laserscribe and subsequent plasma etch may be implemented for diesingulation. The laser scribe process may be used to cleanly remove amask layer, organic and inorganic dielectric layers, and device layers.The laser etch process may then be terminated upon exposure of, orpartial etch of, the wafer or substrate. The plasma etch portion of thedicing process may then be employed to etch through the bulk of thewafer or substrate, such as through bulk single crystalline silicon, toyield die or chip singulation or dicing.

Conventional wafer dicing approaches include diamond saw cutting basedon a purely mechanical separation, initial laser scribing and subsequentdiamond saw dicing, or nanosecond or picosecond laser dicing. For thinwafer or substrate singulation, such as 50 microns thick bulk siliconsingulation, the conventional approaches have yielded only poor processquality. Some of the challenges that may be faced when singulating diefrom thin wafers or substrates may include microcrack formation ordelamination between different layers, chipping of inorganic dielectriclayers, retention of strict kerf width control, or precise ablationdepth control. Embodiments of the present invention include a hybridlaser scribing and plasma etching die singulation approach that may beuseful for overcoming one or more of the above challenges.

In accordance with an embodiment of the present invention, a combinationof femtosecond-based laser scribing and plasma etching is used to dice asemiconductor wafer into individualized or singulated integratedcircuits. In one embodiment, femtosecond-based laser scribing is used asan essentially, if not totally, non-thermal process. For example, thefemtosecond-based laser scribing may be localized with no or negligibleheat damage zone. In an embodiment, approaches herein are used tosingulated integrated circuits having ultra-low k films. With conventiondicing, saws may need to be slowed down to accommodate such low k films.Furthermore, semiconductor wafers are now often thinned prior to dicing.As such, in an embodiment, a combination of mask patterning and partialwafer scribing with a femtosecond-based laser, followed by a plasma etchprocess, is now practical. In one embodiment, direct writing with lasercan eliminate need for a lithography patterning operation of aphoto-resist layer and can be implemented with very little cost. In oneembodiment, through-via type silicon etching is used to complete thedicing process in a plasma etching environment.

Thus, in an aspect of the present invention, a combination offemtosecond-based laser scribing and plasma etching may be used to dicea semiconductor wafer into singulated integrated circuits. FIG. 1illustrates a top plan of a semiconductor wafer to be diced, inaccordance with an embodiment of the present invention. FIG. 2illustrates a top plan of a semiconductor wafer to be diced that has adicing mask formed thereon, in accordance with an embodiment of thepresent invention.

Referring to FIG. 1, a semiconductor wafer 100 has a plurality ofregions 102 that include integrated circuits. The regions 102 areseparated by vertical streets 104 and horizontal streets 106. Thestreets 104 and 106 are areas of semiconductor wafer that do not containintegrated circuits and are designed as locations along which the waferwill be diced. Some embodiments of the present invention involve the useof a combination femtosecond-based laser scribe and plasma etchtechnique to cut trenches through the semiconductor wafer along thestreets such that the dice are separated into individual chips or die.Since both a laser scribe and a plasma etch process are crystalstructure orientation independent, the crystal structure of thesemiconductor wafer to be diced may be immaterial to achieving avertical trench through the wafer.

Referring to FIG. 2, the semiconductor wafer 100 has a mask 200deposited upon the semiconductor wafer 100. In one embodiment, the maskis deposited in a conventional manner to achieve an approximately 4-10micron thick layer. The mask 200 and a portion of the semiconductorwafer 100 are patterned with a laser scribing process to define thelocations (e.g., gaps 202 and 204) along the streets 104 and 106 wherethe semiconductor wafer 100 will be diced. The integrated circuitregions of the semiconductor wafer 100 are covered and protected by themask 200. The regions 206 of the mask 200 are positioned such thatduring a subsequent etching process, the integrated circuits are notdegraded by the etch process. Horizontal gaps 204 and vertical gaps 202are formed between the regions 206 to define the areas that will beetched during the etching process to finally dice the semiconductorwafer 100.

FIG. 3 is a Flowchart 300 representing operations in a method of dicinga semiconductor wafer including a plurality of integrated circuits, inaccordance with an embodiment of the present invention. FIGS. 4A-4Cillustrate cross-sectional views of a semiconductor wafer including aplurality of integrated circuits during performing of a method of dicingthe semiconductor wafer, corresponding to operations of Flowchart 300,in accordance with an embodiment of the present invention.

Referring to operation 302 of Flowchart 300, and corresponding FIG. 4A,a mask 402 is formed above a semiconductor wafer or substrate 404. Themask 402 is composed of a layer covering and protecting integratedcircuits 406 formed on the surface of semiconductor wafer 404. The mask402 also covers intervening streets 407 formed between each of theintegrated circuits 406.

In accordance with an embodiment of the present invention, forming themask 402 includes forming a layer such as, but not limited to, aphoto-resist layer or an I-line patterning layer. For example, a polymerlayer such as a photo-resist layer may be composed of a materialotherwise suitable for use in a lithographic process. In one embodiment,the photo-resist layer is composed of a positive photo-resist materialsuch as, but not limited to, a 248 nanometer (nm) resist, a 193 nmresist, a 157 nm resist, an extreme ultra-violet (EUV) resist, or aphenolic resin matrix with a diazonaphthoquinone sensitizer. In anotherembodiment, the photo-resist layer is composed of a negativephoto-resist material such as, but not limited to, poly-cis-isoprene andpoly-vinyl-cinnamate.

In an embodiment, semiconductor wafer or substrate 404 is composed of amaterial suitable to withstand a fabrication process and upon whichsemiconductor processing layers may suitably be disposed. For example,in one embodiment, semiconductor wafer or substrate 404 is composed of agroup IV-based material such as, but not limited to, crystallinesilicon, germanium or silicon/germanium. In a specific embodiment,providing semiconductor wafer 404 includes providing a monocrystallinesilicon substrate. In a particular embodiment, the monocrystallinesilicon substrate is doped with impurity atoms. In another embodiment,semiconductor wafer or substrate 404 is composed of a III-V materialsuch as, e.g., a III-V material substrate used in the fabrication oflight emitting diodes (LEDs).

In an embodiment, semiconductor wafer or substrate 404 has disposedthereon or therein, as a portion of the integrated circuits 406, anarray of semiconductor devices. Examples of such semiconductor devicesinclude, but are not limited to, memory devices or complimentarymetal-oxide-semiconductor (CMOS) transistors fabricated in a siliconsubstrate and encased in a dielectric layer. A plurality of metalinterconnects may be formed above the devices or transistors, and insurrounding dielectric layers, and may be used to electrically couplethe devices or transistors to form the integrated circuits 406.Materials making up the streets 407 may be similar to or the same asthose materials used to form the integrated circuits 406. For example,streets 407 may be composed of layers of dielectric materials,semiconductor materials, and metallization. In one embodiment, one ormore of the streets 407 includes test devices similar to the actualdevices of the integrated circuits 406.

Referring to operation 304 of Flowchart 300, and corresponding FIG. 4B,the mask 402 is patterned with a femtosecond-based laser scribingprocess to provide a patterned mask 408 with gaps 410, exposing regionsof the semiconductor wafer or substrate 404 between the integratedcircuits 406. As such, the femtosecond-based laser scribing process isused to remove the material of the streets 407 originally formed betweenthe integrated circuits 406. In accordance with an embodiment of thepresent invention, patterning the mask 402 with the femtosecond-basedlaser scribing process includes forming trenches 412 partially into theregions of the semiconductor wafer 404 between the integrated circuits406, as depicted in FIG. 4B.

In an embodiment, patterning the mask 406 with the laser scribingprocess includes using a laser having a pulse width in the femtosecondrange. Specifically, a laser with a wavelength in the visible spectrumplus the ultra-violet (UV) and infra-red (IR) ranges (totaling abroadband optical spectrum) may be used to provide a femtosecond-basedlaser, i.e., a laser with a pulse width on the order of the femtosecond(10⁻¹⁵ seconds). In one embodiment, ablation is not, or is essentiallynot, wavelength dependent and is thus suitable for complex films such asfilms of the mask 402, the streets 407 and, possibly, a portion of thesemiconductor wafer or substrate 404.

FIG. 5 illustrates the effects of using a laser pulse in the femtosecondrange versus longer frequencies, in accordance with an embodiment of thepresent invention. Referring to FIG. 5, by using a laser with a pulsewidth in the femtosecond range heat damage issues are mitigated oreliminated (e.g., minimal to no damage 502C with femtosecond processingof a via 500C) versus longer pulse widths (e.g., damage 502B withpicosecond processing of a via 500B and significant damage 502A withnanosecond processing of a via 500A). The elimination or mitigation ofdamage during formation of via 500C may be due to a lack of low energyrecoupling (as is seen for picosecond-based laser ablation) or thermalequilibrium (as is seen for nanosecond-based laser ablation), asdepicted in FIG. 5.

Laser parameters selection, such as pulse width, may be critical todeveloping a successful laser scribing and dicing process that minimizeschipping, microcracks and delamination in order to achieve clean laserscribe cuts. The cleaner the laser scribe cut, the smoother an etchprocess that may be performed for ultimate die singulation. Insemiconductor device wafers, many functional layers of differentmaterial types (e.g., conductors, insulators, semiconductors) andthicknesses are typically disposed thereon. Such materials may include,but are not limited to, organic materials such as polymers, metals, orinorganic dielectrics such as silicon dioxide and silicon nitride.

A street between individual integrated circuits disposed on a wafer orsubstrate may include the similar or same layers as the integratedcircuits themselves. For example, FIG. 6 illustrates a cross-sectionalview of a stack of materials that may be used in a street region of asemiconductor wafer or substrate, in accordance with an embodiment ofthe present invention.

Referring to FIG. 6, a street region 600 includes the top portion 602 ofa silicon substrate, a first silicon dioxide layer 604, a first etchstop layer 606, a first low K dielectric layer 608 (e.g., having adielectric constant of less than the dielectric constant of 4.0 forsilicon dioxide), a second etch stop layer 610, a second low Kdielectric layer 612, a third etch stop layer 614, an undoped silicaglass (USG) layer 616, a second silicon dioxide layer 618, and a layerof photo-resist 620, with relative thicknesses depicted. Coppermetallization 622 is disposed between the first and third etch stoplayers 606 and 614 and through the second etch stop layer 610. In aspecific embodiment, the first, second and third etch stop layers 606,610 and 614 are composed of silicon nitride, while low K dielectriclayers 608 and 612 are composed of a carbon-doped silicon oxidematerial.

Under conventional laser irradiation (such as nanosecond-based orpicosecond-based laser irradiation), the materials of street 600 behavequite differently in terms of optical absorption and ablationmechanisms. For example, dielectrics layers such as silicon dioxide, isessentially transparent to all commercially available laser wavelengthsunder normal conditions. By contrast, metals, organics (e.g., low Kmaterials) and silicon can couple photons very easily, particularly inresponse to nanosecond-based or picosecond-based laser irradiation. Forexample, FIG. 7 includes a plot 700 of absorption coefficient as afunction of photon energy for crystalline silicon (c-Si, 702), copper(Cu, 704), crystalline silicon dioxide (c-SiO2, 706), and amorphoussilicon dioxide (a-SiO2, 708), in accordance with an embodiment of thepresent invention. FIG. 8 is an equation 800 showing the relationship oflaser intensity for a given laser as a function of laser pulse energy,laser pulse width, and laser beam radius.

Using equation 800 and the plot 700 of absorption coefficients, in anembodiment, parameters for a femtosecond laser-based process may beselected to have an essentially common ablation effect on the inorganicand organic dielectrics, metals, and semiconductors even though thegeneral energy absorption characteristics of such materials may differwidely under certain conditions. For example, the absorptivity ofsilicon dioxide is non-linear and may be brought more in-line with thatof organic dielectrics, semiconductors and metals under the appropriatelaser ablation parameters. In one such embodiment, a high intensity andshort pulse width femtosecond-based laser process is used to ablate astack of layers including a silicon dioxide layer and one or more of anorganic dielectric, a semiconductor, or a metal. In a specificembodiment, pulses of approximately less than or equal to 400femtoseconds are used in a femtosecond-based laser irradiation processto remove a mask, a street, and a portion of a silicon substrate.

By contrast, if non-optimal laser parameters are selected, in a stackedstructures that involve two or more of an inorganic dielectric, anorganic dielectric, a semiconductor, or a metal, a laser ablationprocess may cause delamination issues. For example, a laser penetratethrough high bandgap energy dielectrics (such as silicon dioxide with anapproximately of 9 eV bandgap) without measurable absorption. However,the laser energy may be absorbed in an underlying metal or siliconlayer, causing significant vaporization of the metal or silicon layers.The vaporization may generate high pressures to lift-off the overlyingsilicon dioxide dielectric layer and potentially causing severeinterlayer delamination and microcracking. In an embodiment, whilepicoseconds-based laser irradiation processes lead to microcracking anddelaminating in complex stacks, femtosecond-based laser irradiationprocesses have been demonstrated to not lead to microcracking ordelamination of the same material stacks.

In order to be able to directly ablate dielectric layers, ionization ofthe dielectric materials may need to occur such that they behave similarto a conductive material by strongly absorbing photons. The absorptionmay block a majority of the laser energy from penetrating through tounderlying silicon or metal layers before ultimate ablation of thedielectric layer. In an embodiment, ionization of inorganic dielectricsis feasible when the laser intensity is sufficiently high to initiatephoton-ionization and impact ionization in the inorganic dielectricmaterials.

In accordance with an embodiment of the present invention, suitablefemtosecond-based laser processes are characterized by a high peakintensity (irradiance) that usually leads to nonlinear interactions invarious materials. In one such embodiment, the femtosecond laser sourceshave a pulse width approximately in the range of 10 femtoseconds to 500femtoseconds, although preferably in the range of 100 femtoseconds to400 femtoseconds. In one embodiment, the femtosecond laser sources havea wavelength approximately in the range of 1570 nanometers to 200nanometers, although preferably in the range of 540 nanometers to 250nanometers. In one embodiment, the laser and corresponding opticalsystem provide a focal spot at the work surface approximately in therange of 3 microns to 15 microns, though preferably approximately in therange of 5 microns to 10 microns.

The spacial beam profile at the work surface may be a single mode(Gaussian) or have a shaped top-hat profile. In an embodiment, the lasersource has a pulse repetition rate approximately in the range of 200 kHzto 10 MHz, although preferably approximately in the range of 500 kHz to5 MHz. In an embodiment, the laser source delivers pulse energy at thework surface approximately in the range of 0.5 uJ to 100 uJ, althoughpreferably approximately in the range of 1 uJ to 5 uJ. In an embodiment,the laser scribing process runs along a work piece surface at a speedapproximately in the range of 500 mm/sec to 5 m/sec, although preferablyapproximately in the range of 600 mm/sec to 2 m/sec.

The scribing process may be run in single pass only, or in multiplepasses, but, in an embodiment, preferably 1-2 passes. In one embodiment,the scribing depth in the work piece is approximately in the range of 5microns to 50 microns deep, preferably approximately in the range of 10microns to 20 microns deep. The laser may be applied either in a trainof single pulses at a given pulse repetition rate or a train of pulsebursts. In an embodiment, the kerf width of the laser beam generated isapproximately in the range of 2 microns to 15 microns, although insilicon wafer scribing/dicing preferably approximately in the range of 6microns to 10 microns, measured at the device/silicon interface.

Laser parameters may be selected with benefits and advantages such asproviding sufficiently high laser intensity to achieve ionization ofinorganic dielectrics (e.g., silicon dioxide) and to minimizedelamination and chipping caused by underlayer damage prior to directablation of inorganic dielectrics. Also, parameters may be selected toprovide meaningful process throughput for industrial applications withprecisely controlled ablation width (e.g., kerf width) and depth. Asdescribed above, a femtosecond-based laser is far more suitable toproviding such advantages, as compared with picosecond-based andnanosecond-based laser ablation processes. However, even in the spectrumof femtosecond-based laser ablation, certain wavelengths may providebetter performance than others. For example, in one embodiment, afemtosecond-based laser process having a wavelength closer to or in theUV range provides a cleaner ablation process than a femtosecond-basedlaser process having a wavelength closer to or in the IR range. In aspecific such embodiment, a femtosecond-based laser process suitable forsemiconductor wafer or substrate scribing is based on a laser having awavelength of approximately less than or equal to 540 nanometers. In aparticular such embodiment, pulses of approximately less than or equalto 400 femtoseconds of the laser having the wavelength of approximatelyless than or equal to 540 nanometers are used. However, in analternative embodiment, dual laser wavelengths (e.g., a combination ofan IR laser and a UV laser) are used.

Referring to operation 306 of Flowchart 300, and corresponding FIG. 4C,the semiconductor wafer 404 is etched through the gaps 410 in thepatterned mask 408 to singulate the integrated circuits 406. Inaccordance with an embodiment of the present invention, etching thesemiconductor wafer 404 includes etching the trenches 412 formed withthe femtosecond-based laser scribing process to ultimately etch entirelythrough semiconductor wafer 404, as depicted in FIG. 4C.

In an embodiment, etching the semiconductor wafer 404 includes using aplasma etching process. In one embodiment, a through-silicon via typeetch process is used. For example, in a specific embodiment, the etchrate of the material of semiconductor wafer 404 is greater than 25microns per minute. An ultra-high-density plasma source may be used forthe plasma etching portion of the die singulation process. An example ofa process chamber suitable to perform such a plasma etch process is theApplied Centura® Silvia™ Etch system available from Applied Materials ofSunnyvale, Calif., USA. The Applied Centura® Silvia™ Etch systemcombines the capacitive and inductive RF coupling, which gives much moreindependent control of the ion density and ion energy than was possiblewith the capacitive coupling only, even with the improvements providedby magnetic enhancement. This combination enables effective decouplingof the ion density from ion energy, so as to achieve relatively highdensity plasmas without the high, potentially damaging, DC bias levels,even at very low pressures. This results in an exceptionally wideprocess window. However, any plasma etch chamber capable of etchingsilicon may be used. In an exemplary embodiment, a deep silicon etch isused to etch a single crystalline silicon substrate or wafer 404 at anetch rate greater than approximately 40% of conventional silicon etchrates while maintaining essentially precise profile control andvirtually scallop-free sidewalls. In a specific embodiment, athrough-silicon via type etch process is used. The etch process is basedon a plasma generated from a reactive gas, which generally afluorine-based gas such as SF₆, C₄ F₈, CHF₃, XeF₂, or any other reactantgas capable of etching silicon at a relatively fast etch rate. In anembodiment, the mask layer 408 is removed after the singulation process,as depicted in FIG. 4C.

Accordingly, referring again to Flowchart 300 and FIGS. 4A-4C, waferdicing may be preformed by initial laser ablation through a mask layer,through wafer streets (including metallization), and partially into asilicon substrate. The laser pulse width may be selected in thefemtosecond range. Die singulation may then be completed by subsequentthrough-silicon deep plasma etching. A specific example of a materialsstack for dicing is described below in association with FIGS. 9A-9D, inaccordance with an embodiment of the present invention.

Referring to FIG. 9A, a materials stack for hybrid laser ablation andplasma etch dicing includes a mask layer 902, a device layer 904, and asubstrate 906. The mask layer, device layer, and substrate are disposedabove a die attach film 908 which is affixed to a backing tape 910. Inan embodiment, the mask layer 902 is a photo-resist layer such as thephoto-resist layers described above in association with mask 402. Thedevice layer 904 includes an inorganic dielectric layer (such as silicondioxide) disposed above one or more metal layers (such as copper layers)and one or more low K dielectric layers (such as carbon-doped oxidelayers). The device layer 904 also includes streets arranged betweenintegrated circuits, the streets including the same or similar layers tothe integrated circuits. The substrate 906 is a bulk single-crystallinesilicon substrate.

In an embodiment, the bulk single-crystalline silicon substrate 906 isthinned from the backside prior to being affixed to the die attach film908. The thinning may be performed by a backside grind process. In oneembodiment, the bulk single-crystalline silicon substrate 906 is thinnedto a thickness approximately in the range of 50-100 microns. It isimportant to note that, in an embodiment, the thinning is performedprior to a laser ablation and plasma etch dicing process. In anembodiment, the photo-resist layer 902 has a thickness of approximately5 microns and the device layer 904 has a thickness approximately in therange of 2-3 microns. In an embodiment, the die attach film 908 (or anysuitable substitute capable of bonding a thinned or thin wafer orsubstrate to the backing tape 910) has a thickness of approximately 20microns.

Referring to FIG. 9B, the mask 902, the device layer 904 and a portionof the substrate 906 are patterned with a femtosecond-based laserscribing process 912 to form trenches 914 in the substrate 906.Referring to FIG. 9C, a through-silicon deep plasma etch process 916 isused to extend the trench 914 down to the die attach film 908, exposingthe top portion of the die attach film 908 and singulating the siliconsubstrate 906. The device layer 904 is protected by the photo-resistlayer 902 during the through-silicon deep plasma etch process 916.

Referring to FIG. 9D, the singulation process may further includepatterning the die attach film 908, exposing the top portion of thebacking tape 910 and singulating the die attach film 908. In anembodiment, the die attach film is singulated by a laser process or byan etch process. Further embodiments may include subsequently removingthe singulated portions of substrate 906 (e.g., as individual integratedcircuits) from the backing tape 910. In one embodiment, the singulateddie attach film 908 is retained on the back sides of the singulatedportions of substrate 906. Other embodiments may include removing themasking photo-resist layer 902 from the device layer 904. In analternative embodiment, in the case that substrate 906 is thinner thanapproximately 50 microns, the laser ablation process 912 is used tocompletely singulate substrate 906 without the use of an additionalplasma process.

Subsequent to singulating the die attach film 908, in an embodiment, themasking photo-resist layer 902 is removed from the device layer 904. Inan embodiment, the singulated integrated circuits are removed from thebacking tape 910 for packaging. In one such embodiment, the patterneddie attach film 908 is retained on the backside of each integratedcircuit and included in the final packaging. However, in anotherembodiment, the patterned die attach film 908 is removed during orsubsequent to the singulation process.

Referring again to FIGS. 4A-4C, the plurality of integrated circuits 406may be separated by streets 407 having a width of approximately 10microns or smaller. The use of a femtosecond-based laser scribingapproach, at least in part due to the tight profile control of thelaser, may enable such compaction in a layout of integrated circuits.For example, FIG. 10 illustrates compaction on a semiconductor wafer orsubstrate achieved by using narrower streets versus conventional dicingwhich may be limited to a minimum width, in accordance with anembodiment of the present invention.

Referring to FIG. 10, compaction on a semiconductor wafer is achieved byusing narrower streets (e.g., widths of approximately 10 microns orsmaller in layout 1002) versus conventional dicing which may be limitedto a minimum width (e.g., widths of approximately 70 microns or largerin layout 1000). It is to be understood, however, that it may not alwaysbe desirable to reduce the street width to less than 10 microns even ifotherwise enabled by a femtosecond-based laser scribing process. Forexample, some applications may require a street width of at least 40microns in order to fabricate dummy or test devices in the streetsseparating the integrated circuits.

Referring again to FIGS. 4A-4C, the plurality of integrated circuits 406may be arranged on semiconductor wafer or substrate 404 in anon-restricted layout. For example, FIG. 11 illustrates freeformintegrated circuit arrangement allowing denser packing. The denserpacking may provide for more die per wafer versus grid alignmentapproaches, in accordance with an embodiment of the present invention.Referring to FIG. 11, a freeform layout (e.g., a non-restricted layouton semiconductor wafer or substrate 1102) allows denser packing andhence more die per wafer versus grid alignment approaches (e.g., arestricted layout on semiconductor wafer or substrate 1100). In anembodiment, the speed of the laser ablation and plasma etch singulationprocess is independent of die size, layout or the number of streets.

A single process tool may be configured to perform many or all of theoperations in a hybrid femtosecond-based laser ablation and plasma etchsingulation process. For example, FIG. 12 illustrates a block diagram ofa tool layout for laser and plasma dicing of wafers or substrates, inaccordance with an embodiment of the present invention.

Referring to FIG. 12, a process tool 1200 includes a factory interface1202 (FI) having a plurality of load locks 1204 coupled therewith. Acluster tool 1206 is coupled with the factory interface 1202. Thecluster tool 1206 includes one or more plasma etch chambers, such asplasma etch chamber 1208. A laser scribe apparatus 1210 is also coupledto the factory interface 1202. The overall footprint of the process tool1200 may be, in one embodiment, approximately 3500 millimeters (3.5meters) by approximately 3800 millimeters (3.8 meters), as depicted inFIG. 12.

In an embodiment, the laser scribe apparatus 1210 houses afemtosecond-based laser. The femtosecond-based laser is suitable forperforming a laser ablation portion of a hybrid laser and etchsingulation process, such as the laser abalation processes describedabove. In one embodiment, a moveable stage is also included in laserscribe apparatus 1200, the moveable stage configured for moving a waferor substrate (or a carrier thereof) relative to the femtosecond-basedlaser. In a specific embodiment, the femtosecond-based laser is alsomoveable. The overall footprint of the laser scribe apparatus 1210 maybe, in one embodiment, approximately 2240 millimeters by approximately1270 millimeters, as depicted in FIG. 12.

In an embodiment, the one or more plasma etch chambers 1208 isconfigured for etching a wafer or substrate through the gaps in apatterned mask to singulate a plurality of integrated circuits. In onesuch embodiment, the one or more plasma etch chambers 1208 is configuredto perform a deep silicon etch process. In a specific embodiment, theone or more plasma etch chambers 1208 is an Applied Centura® Silvia™Etch system, available from Applied Materials of Sunnyvale, Calif., USA.The etch chamber may be specifically designed for a deep silicon etchused to create singulate integrated circuits housed on or in singlecrystalline silicon substrates or wafers. In an embodiment, ahigh-density plasma source is included in the plasma etch chamber 1208to facilitate high silicon etch rates. In an embodiment, more than oneetch chamber is included in the cluster tool 1206 portion of processtool 1200 to enable high manufacturing throughput of the singulation ordicing process.

The factory interface 1202 may be a suitable atmospheric port tointerface between an outside manufacturing facility with laser scribeapparatus 1210 and cluster tool 1206. The factory interface 1202 mayinclude robots with arms or blades for transferring wafers (or carriersthereof) from storage units (such as front opening unified pods) intoeither cluster tool 1206 or laser scribe apparatus 1210, or both.

Cluster tool 1206 may include other chambers suitable for performingfunctions in a method of singulation. For example, in one embodiment, inplace of an additional etch chamber, a deposition chamber 1212 isincluded. The deposition chamber 1212 may be configured for maskdeposition on or above a device layer of a wafer or substrate prior tolaser scribing of the wafer or substrate. In one such embodiment, thedeposition chamber 1212 is suitable for depositing a photo-resist layer.In another embodiment, in place of an additional etch chamber, a wet/drystation 1214 is included. The wet/dry station may be suitable forcleaning residues and fragments, or for removing a mask, subsequent to alaser scribe and plasma etch singulation process of a substrate orwafer. In an embodiment, a metrology station is also included as acomponent of process tool 1200.

Embodiments of the present invention may be provided as a computerprogram product, or software, that may include a machine-readable mediumhaving stored thereon instructions, which may be used to program acomputer system (or other electronic devices) to perform a processaccording to embodiments of the present invention. In one embodiment,the computer system is coupled with process tool 1200 described inassociation with FIG. 12. A machine-readable medium includes anymechanism for storing or transmitting information in a form readable bya machine (e.g., a computer). For example, a machine-readable (e.g.,computer-readable) medium includes a machine (e.g., a computer) readablestorage medium (e.g., read only memory (“ROM”), random access memory(“RAM”), magnetic disk storage media, optical storage media, flashmemory devices, etc.), a machine (e.g., computer) readable transmissionmedium (electrical, optical, acoustical or other form of propagatedsignals (e.g., infrared signals, digital signals, etc.)), etc.

FIG. 13 illustrates a diagrammatic representation of a machine in theexemplary form of a computer system 1300 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies described herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a Local Area Network (LAN), an intranet, an extranet, or theInternet. The machine may operate in the capacity of a server or aclient machine in a client-server network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, switch or bridge, or any machinecapable of executing a set of instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies described herein.

The exemplary computer system 1300 includes a processor 1302, a mainmemory 1304 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 1306 (e.g., flash memory, static randomaccess memory (SRAM), etc.), and a secondary memory 1318 (e.g., a datastorage device), which communicate with each other via a bus 1330.

Processor 1302 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processor 1302 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processor 1302 may alsobe one or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or thelike. Processor 1302 is configured to execute the processing logic 1326for performing the operations described herein.

The computer system 1300 may further include a network interface device1308. The computer system 1300 also may include a video display unit1310 (e.g., a liquid crystal display (LCD), a light emitting diodedisplay (LED), or a cathode ray tube (CRT)), an alphanumeric inputdevice 1312 (e.g., a keyboard), a cursor control device 1314 (e.g., amouse), and a signal generation device 1316 (e.g., a speaker).

The secondary memory 1318 may include a machine-accessible storagemedium (or more specifically a computer-readable storage medium) 1331 onwhich is stored one or more sets of instructions (e.g., software 1322)embodying any one or more of the methodologies or functions describedherein. The software 1322 may also reside, completely or at leastpartially, within the main memory 1304 and/or within the processor 1302during execution thereof by the computer system 1300, the main memory1304 and the processor 1302 also constituting machine-readable storagemedia. The software 1322 may further be transmitted or received over anetwork 1320 via the network interface device 1308.

While the machine-accessible storage medium 1331 is shown in anexemplary embodiment to be a single medium, the term “machine-readablestorage medium” should be taken to include a single medium or multiplemedia (e.g., a centralized or distributed database, and/or associatedcaches and servers) that store the one or more sets of instructions. Theterm “machine-readable storage medium” shall also be taken to includeany medium that is capable of storing or encoding a set of instructionsfor execution by the machine and that cause the machine to perform anyone or more of the methodologies of the present invention. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, and optical and magneticmedia.

In accordance with an embodiment of the present invention, amachine-accessible storage medium has instructions stored thereon whichcause a data processing system to perform a method of dicing asemiconductor wafer having a plurality of integrated circuits. Themethod includes forming a mask above the semiconductor wafer, the maskcomposed of a layer covering and protecting the integrated circuits. Themask is then patterned with a femtosecond-based laser scribing processto provide a patterned mask with gaps. Regions of the semiconductorwafer are exposed between the integrated circuits. The semiconductorwafer is then etched through the gaps in the patterned mask to singulatethe integrated circuits.

Thus, methods of dicing semiconductor wafers, each wafer having aplurality of integrated circuits, have been disclosed. In accordancewith an embodiment of the present invention, a method includes dicing asemiconductor wafer having a plurality of integrated circuits includesforming a mask above the semiconductor wafer, the mask composed of alayer covering and protecting the integrated circuits. The method alsoincludes patterning the mask with a femtosecond-based laser scribingprocess to provide a patterned mask with gaps, exposing regions of thesemiconductor wafer between the integrated circuits. The method alsoincludes etching the semiconductor wafer through the gaps in thepatterned mask to singulate the integrated circuits. In one embodiment,patterning the mask with the femtosecond-based laser scribing processincludes forming trenches in the regions of the semiconductor waferbetween the integrated circuits. In that embodiment, etching thesemiconductor wafer includes etching the trenches formed with the laserscribing process.

1. A method of dicing a semiconductor wafer comprising a plurality ofintegrated circuits, the method comprising: forming a mask above thesemiconductor wafer, the mask comprising a layer covering and protectingthe integrated circuits; patterning the mask with a femtosecond-basedlaser scribing process to provide a patterned mask with gaps, exposingregions of the semiconductor wafer between the integrated circuits; andetching the semiconductor wafer through the gaps in the patterned maskto singulate the integrated circuits.
 2. The method of claim 1, whereinpatterning the mask with the femtosecond-based laser scribing processcomprises forming trenches in the regions of the semiconductor waferbetween the integrated circuits, and etching the semiconductor wafercomprises etching the trenches formed with the femtosecond-based laserscribing process.
 3. The method of claim 1, wherein patterning the maskwith the femtosecond-based laser scribing process comprises using alaser having a wavelength of approximately less than or equal to 540nanometers with a laser pulse width of approximately less than or equalto 400 femtoseconds.
 4. The method of claim 1, wherein etching thesemiconductor wafer comprises using a high density plasma etchingprocess.
 5. The method of claim 1, wherein forming the mask comprisesforming a layer selected from the group consisting of a photo-resistlayer and an Mine patterning layer.
 6. The method of claim 1, whereinthe plurality of integrated circuits is separated by streets having awidth of approximately 10 microns or smaller as measured at a devicelayer/substrate interface.
 7. The method of claim 1, wherein theplurality of integrated circuits has a non-restricted layout.
 8. Asystem for dicing a semiconductor wafer comprising a plurality ofintegrated circuits, the system comprising: a factory interface; a laserscribe apparatus coupled with the factory interface and comprising afemtosecond-based laser; and a plasma etch chamber coupled with thefactory interface.
 9. The system of claim 8, wherein the laser scribeapparatus is configured to perform laser ablation of streets betweenintegrated circuits of a semiconductor wafer, and wherein the plasmaetch chamber is configured to etch the semiconductor wafer to singulatethe integrated circuits subsequent to the laser ablation.
 10. The systemof claim 9, wherein the plasma etch chamber is housed on a cluster toolcoupled with the factory interface, the cluster tool further comprising:a deposition chamber configured to form a mask layer above theintegrated circuits of the semiconductor wafer.
 11. The system of claim9, wherein the plasma etch chamber housed on a cluster tool coupled withthe factory interface, the cluster tool further comprising: a wet/drystation configured to clean the semiconductor wafer subsequent to thelaser ablation or the etching.
 12. The system of claim 8, wherein thefemtosecond-based laser has a wavelength of approximately less than orequal to 530 nanometers with a laser pulse width of approximately lessthan or equal to 400 femtoseconds.
 13. The system of claim 8, whereinplasma etch chamber is configured to generate a high density plasma. 14.The system of claim 10, wherein the deposition chamber is configured todeposit a polymer layer.
 15. A method of dicing a semiconductor wafercomprising a plurality of integrated circuits, the method comprising:forming a polymer layer above a silicon substrate, the polymer layercovering and protecting integrated circuits disposed on the siliconsubstrate, the integrated circuits comprising a layer of silicon dioxidedisposed above a layer of low K material and a layer of copper;patterning the polymer layer, the layer of silicon dioxide, the layer oflow K material, and the layer of copper with a femtosecond-based laserscribing process to expose regions of the silicon substrate between theintegrated circuits; and etching the silicon substrate through the gapsto singulate the integrated circuits.
 16. The method of claim 15,wherein patterning the layer of silicon dioxide, the layer of low Kmaterial, and the layer of copper with the femtosecond-based laserscribing process comprises ablating the layer of silicon dioxide priorto ablating the layer of low K material and the layer of copper.
 17. Themethod of claim 15, wherein patterning with the femtosecond-based laserscribing process further comprises forming trenches in the regions ofthe silicon substrate between the integrated circuits, and etching thesilicon substrate comprises etching the trenches formed with thefemtosecond-based laser scribing process.
 18. The method of claim 15,wherein the patterning with the femtosecond-based laser scribing processcomprises using a laser having a wavelength of approximately less thanor equal to 530 nanometers with a laser pulse width of approximatelyless than or equal to 400 femtoseconds.
 19. The method of claim 15,wherein etching the silicon substrate comprises using a high densitythrough-silicon plasma etching process.
 20. The method of claim 15,wherein the integrated circuits are separated by streets having a widthof approximately 10 microns or smaller.